1. Field of the Invention
This invention relates to drill bits, and, more particularly, to drill bits normally used for drilling in concrete and the like.
2. Description of the Prior Art
Prior art drill bits typically used to drill in concrete and the like, and which are used in pneumatic drills, generally include a rear base having flats adapted to secure the drill bit in a drill chuck. The end of the drill bit or drill steel, as it is sometimes referred to, is impacted by a piston pneumatically actuated in the pneumatic drill. The repetitive hammering by the drill bit, or by the point of the drill element, then fractures or chips away the concrete to make a hole. The drill steel rotates as it impacts in the concrete.
The drill steel or drill bit generally includes a bore through which compressed air flows to the bit portion at the tip of the drill bit for purposes of cleaning out the hole being made by the drill tip. The bit portion generally has a slightly larger diameter than does the stem, and there are typically flutes or slots in the bit portion through which the debris from the concrete being drilled is expelled rearwardly and out of the hole being drilled.
Typically, the bit portion consists of a plurality of tip elements using carbide points or tips perform the actual drilling or cutting operation. There may be four or six or more such carbide tips, depending on the particular drill bit design.
There may be slight variations of the drill bit described in the preceding paragraphs. However, there have been no substantial changes in the basic drill bit or drill elements since the advent of pneumatic drill many decades ago. Obviously, there will be differences in lengths and in the diameters of the drill bits, depending on the size of the drills used and the holes to be drilled, both in terms of diameter and length, and there may be variations due to a particular chuck design or due to the size of the pneumatic drill to which the drill bit or steel will be secured.
The carbide drill tips generally wear out long before the rest of the drill bit wears out. In some cases, the carbide tipes may be replaced, but more generally the entire drill bit is discarded in favor of a new drill bit.
When a rock is encountered in drilling a hole, the tendency of the drill bit is to veer away from the rock and to take the path of least resistance, or an area where a rock is not encountered. This, of course, effects the accuracy of the hole being drilled, and is accordingly an undesirable occurrence.
U.S. Pat. No. 1,746,455 (Woodruff et al) discloses a drill bit which includes a pilot blade disposed centrally between a plurality of cutting blades. The pilot blade rotates through a multi-stepped cam system.
U.S. Pat. No. 2,080,526 (Bedford) discloses a device for holding a drill bit. The apparatus includes a socket system which includes air passages, both axially extending and radially extending.
U.S. Pat. No. 2,191,699 (Stephens) discloses a rock drill which includes a threaded engagement between the drill shank and a drill bit.
U.S. Pat. No. 3,047,082 (Brown) discloses a masonry drill designed particularly for use in a hand-held pneumatic drill. The drill includes a particular tip design. The specific design of the tip enhances the use of the apparatus in drilling concrete and the like.
It will be noted that in U.S. Pat. No. 3,047,082 patent there is no provision for the use of compressed air to blow away debris from the hole being drilled, as is present with all of the other drills discussed herein.
U.S. Pat. No. 3,613,807 (Galis) discloses a drill rod designed for use with percussion (pneumatic) type drills. The patent is particularly concerned with the drill tip and with the removal of dust or debris from the hole being drilled. Suction is applied to pull the dust and debris away from the tip, as opposed to the more common compressed air system of blowing the dust and debris out of the hole being drilled.
U.S. Pat. No. 3,682,260 (Klemm) discloses a rotary percussion drill utilizing a plurality of impact elements drilling within a casement. The apparatus is designed for deep vertical drilling in which outer casement members are continuously added as drilling proceeds. A down-the-hole hammer is utilized.
In the apparatus of the present invention, a center, pilot drill is utilized. The pilot drill makes first contact with the concrete to be drilled, and the primary drill, coaxially related to the pilot drill, then impacts the concrete to be drilled. The result is that a hole is drilled more rapidly and more efficiently and more accurately than is possible with the drill bits of the prior art. If or when a rock is encountered, the pilot drill virtually drills straight ahead and thus shatters the rock, and does not allow the primary drill to be moved or to veer away from the rock. Moreover, with the pilot drill centered in the hole being drilled, debris is generally moved out of the way of the primary drill, thus helping to increase the efficiency of the primary drill and of the carbide tip thereon.